我能获得一个＆QUOT;组分QUOT;按类型？ [英] Can I gain access to a "component" by type?

问题描述

我有这样一个类：

class Component1 {...};
class Component2 {...};
class Component3 {...};

class Entity
{
  Component1 c1;
  Component2 c2;
  Component3 c3;
public:
  Component1& get_c1() { return c1;}
  Component2& get_c2() { return c2;}
  Component3& get_c3() { return c3;}
};

基本上是实体的所有可能的类型的组件的容器（与其他的东西，太）。我的问题是，我有超过15个不同的组件和我不喜欢复制和放大器;这样贴线。
我在寻找类似：

Basically the Entity is a container of all possible types of components (with other stuff, too). My problem is that I have more than 15 different components and I don't like to copy&paste lines this way. I'm looking for something like:

myEntity.get<Component1>();

要获得我所需要的组件。我接过一看的boost ::元组是很酷，但它允许访问使用整数的关键。我可以在每个组件*类使用公共静态常量整数，并获得这样的访问：

to obtain the component I need. I took a look at boost::tuple which is cool but it allows access using an integer as key. I could use a public static const integer in each Component* class and gain access like this:

myEntity.get<Component1::id>();

但我必须确保使用不同的ID为每个组件，这就是坏mantainance。

but then I have to make sure to use different ids for each component and that's bad for mantainance.

有没有办法使用魔法（即模板），让图型该类型的值
myEntity.get＆LT;＆的Component1 GT;？（）按预期工作

Is there a way to "map" a type to a value of that type using magic (i.e. templates), so that myEntity.get<Component1>() works as expected?

我也想有，因为O（1）访问组件 myEntity所:: GET＆LT; T＆GT; 与15经常使用（而不是20个组件是有道理反正谈论的复杂性），但是，这不是强制性的。

I'd also like to have O(1) access to a component since the myEntity::get<T> is used very often (not that with 15-20 components makes sense talking about complexity anyway) but that's not mandatory.

推荐答案

我非常接近问同样的问题：我的boost ::融合::地图或的boost ::融合::设为是矫枉过正，我真的不喜欢超长的模板参数列表，不必设置一个宏，如果我有10个以上在我的容器。我有这样的事情了：

I very nearly asked the same question: for me boost::fusion::map or boost::fusion::set are overkill and I really don't like the extra-long template parameter lists and having to set a macro if I have more than 10 in my container. I went with something like this:

template <class T>
struct Holder
{
    T t;
};

struct A {};
struct B {};

struct Aggregate
    :
    Holder<A>, 
    Holder<B>  // add as many more as you need here
{
    template <class T>
    T &get()
    {
        return this->Holder<T>::t;
    }
};

Aggregate a;
a.get<A>();
a.get<B>();

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